This invention relates to a method and apparatus for machining a workpiece, and more particularly to a method and apparatus for machining on a lathe the bearing journal of a rotary drill bit body section or so-called lug.
A rotary drill bit is normally formed of three elongated body sections or lugs which are welded together to form the completed bit body as illustrated generally in U.S. Pat. No. 4,414,734 dated Nov. 15, 1983. Each bit body section has a bearing journal adjacent one end thereof to mount a rotatable roller cutter thereon, and a shank or leg extending from the bearing journal as shown generally in U.S. Pat. No. 4,410,284 dated Oct. 18, 1983. The leg has two so-called one hundred twenty degrees (120.degree.) faces which serve as reference planes for the machining of the bearing journal. Precise machining of the bearing journal is crucial to the useful life of the bearing assembly for the roller cutter, and thus to the overall life of the drill bit.
Heretofore, the fixture or holder for positioning and clamping of a drill bit body section or lug for machining the journal has utilized a pair of gripping jaws fixedly positioned on a rotary lathe. The positioning of the bit body section within such jaws on the lathe was time consuming particularly since a very high degree of accuracy is involved, and oftentimes resulted in a scrapping of a machined body section due to inaccurate alignment during machining operations. All of this is, of course, uneconomical as well as time consuming. In addition, the body section which may weigh fifty (50) pounds or more, could be a safety hazard to a machine operator when loading the bit body section into the turning lathe, as well as in removing the finished body section from the lathe.
Various types of fixtures or holders for rotary drill bit sections or lugs are also shown in U.S. Pat. No. 3,907,191 dated Sept. 23, 1975, and U.S. Pat. No. 4,054,772 dated Oct. 18, 1977.